Refactor lock release and sema up to remove unnecessary code

src/threads/synch.c

@@ -113,6 +113,7 @@ void
 sema_up (struct semaphore *sema)
 {
   enum intr_level old_level;
+  bool thread_unblocked = false; /* Flag to track if any thread was woken up. */
 
   ASSERT (sema != NULL);
 
@@ -124,6 +125,7 @@ sema_up (struct semaphore *sema)
     struct list_elem *e = list_max (&sema->waiters, priority_less, NULL);
     list_remove (e);
     thread_unblock (list_entry (e, struct thread, elem));
+    thread_unblocked = true;
   }
   sema->value++;
   intr_set_level (old_level);
@@ -131,10 +133,13 @@ sema_up (struct semaphore *sema)
   /* Yields the CPU in case the thread that has been woken up has a higher
      priority that the current running thread, including the case when called
      within an interrupt handler. */
+  if (thread_unblocked)
+  {
     if (intr_context ())
       intr_yield_on_return ();
     else
       thread_yield ();
+  }
 }
 
 static void sema_test_helper (void *sema_);
@@ -347,7 +352,6 @@ lock_release (struct lock *lock)
 
   lock->holder = NULL;
   sema_up (&lock->semaphore);
-  thread_yield ();
 }
 
 /* Returns true if the current thread holds LOCK, false